S-Quark_mini QLW "A minimalist ESP32 development board"

### S-Quark mini QLW version

S-Quark mini QLW is based on the evolution of S-Quark mini2. The original CP2104 is replaced by my open source project Quark Link Wireless GitHub open source address is as follows: [https://github.com/Z2Z-GuGu/Quark-Link-Wireless](https://github.com/Z2Z-GuGu/Quark-Link-Wireless). Since the mini2 version BOOT uses a sequential logic circuit to only recognize the DTR/RTS signal, and the TF card occupies the GPIO2 pin after insertion, it is difficult to guarantee the success of BOOT. The QLW version will provide more accurate BOOT mode control than the S-Quark mini2.

Quark Link Wireless is an open source firmware for microcontroller communication developed based on CH573 hardware. In addition to the conventional USB to UART serial port function, QLW also provides USB to BLE, chip BOOT/RESET control, onboard device agent, main chip external pull-up and pull-down resistor configuration and other functions. Currently, the UART data power-off preservation in USB offline state is being developed, and it is expected to store up to 320KByte of information (that is, a 22Byte serial port data is thrown out every 5 minutes, and the QLW hardware system can save it continuously for one month). All functions can be freely configured through UART (AT mode), USB (configuration mode), and BLE (0xFFE1 service).

As the first Quark mini development board with QLW system onboard, it has the following features:

+ PCB features:
+ The width of PCB pin header is maintained at 10 holes and the length is controlled at 17 holes, so it can be easily placed even on a small breadboard;
+ GPIO is arranged counterclockwise from small to large, which is convenient for finding GPIO;
+ GND, +3.3V, and +5V ports are set at the head of the pin headers on both sides of the PCB to facilitate power supply of standard-sized breadboards; +
The entire S-Quark-mini series uses USB Type C as the USB connection port, which is convenient for blind plugging;
+ Onboard suspended TF card holder (single-line SDIO communication) is convenient for repeated plugging and unplugging of TF cards during development, with a simple appearance and taking up little PCB space;
+ The head position adopts the design language of Quark mini, with SYS LED and KEY on the right side of the USB interface; USER LED and KEY on the left side, with a simple and beautiful design and small footprint; +
PSRAM pads are reserved on the back of S-Quark-mini QLW for easy expansion of RAM;
+ Considering that the RF antenna in the QLW system is not in a good position, you can change the patch position to replace the IPEX4 external antenna with a better RF performance.
+ QLW system features:
+ Use SYS LED instead of PWR LED.

In the default state, SYS LED performs the following functions:

1. In normal state, SYS LED is always on, indicating that the power is normal, that is, PWR LED is always on.
2. SYS LED flashes in downloading state.
3. SYS LED flashes twice when USB is disconnected/connected
. 4. Flashes quickly during USB - UART data transmission .
5. When QLW is configured in low power mode, SYS LED is always off and flashes briefly once per second
. 6. SYS LED is always off when QLW system is abnormal.

In addition, the SYS LED status can be controlled by GPIO 0/1/2/3/14/15 and QL pins. You can freely configure whether it is high level or low level to light up, simulating hardware pull-up or pull-down LED.

SYS LED can also be controlled by MCU UART json command, USB json command, BLE json command.

+ Use USER LED instead of GPIO LED.

In the default state, USER LED synchronizes GPIO2 level, that is, GPIO2 high level lights up LED.

USER LED status can be controlled by GPIO 0/1/2/3/14/15, QL pin control, you can freely configure its high level or low level to light up, simulating hardware pull-up or pull-down LED

USER LED can also be controlled by MCU AT commands, USB json commands, BLE json commands

+ Use SYS KEY instead of RST KEY .

In the default state, SYS KEY performs the following functions

1. Short press SYS KEY (within 10s) has the same effect as RST KEY, controls EN pin, and resets ESP32
2. Long press SYS KEY (more than 10s) to restore QLW system configuration and reset ESP32

In addition, SYS KEY can be configured to output switch signals to GPIO 0/1/2/3/14/15, QL pins, and can be freely configured to output high and low levels after pressing, simulating hardware pull-up or pull-down buttons

+ Use USER KEY instead of GPIO KEY.

In the default state, USER KEY outputs a jitter-free switch signal to GPIO0, that is, GPIO0 detects a low level after pressing, and a high level when lifted.

In addition, USER KEY Can be configured to output switch signals to GPIO 0/1/2/3/14/15, QL pins, can be freely configured to output high and low levels after pressing, simulating hardware pull-up or pull-down buttons

USER KEY can be configured to simulate key jitter

+ Take over the pull-up resistor of GPIO2/14/15 (single-line SDIO), and configure it to float GPIO when the SD card is not needed to ensure normal impedance of related pins (officially supported after Rev3.1 Beta1)

+ QL function pin, replaces the GND pin of S-Quark mini2, provides special functions such as debugging, and the default QL pin will float

+ About QLW system configuration: All configuration information can be modified through USB (configuration COM), BLE (Service UUID: 0xFFE0), and UART.

+ Note: The configuration COM in Windows is usually a COM port with a smaller number. The configuration COM name in macOS is "usbmodemQuark_Linker_3". If it is difficult to distinguish, you can send "{"V":"tap"}" to any serial port. The one that replies "{"QLW-V":"Rx"}" is the configuration serial port.
+ QLW desktop configuration software will be provided later, and three versions will be provided for Windows, macOS and Linux.
+ Bluetooth can be used with the help of "Blinker" software to achieve graphical configuration